Bug 1789779 - Work around miscompilation on cross-LTO. r=emilio

Starting from
6c8adc5054,
Servo_NoteExplicitHints can end up inlined in its callers via
cross-language LTO, which didn't happen before. This yields a
miscompilation in the caller, causing crashes. Until the miscompilation
is fixed, avoid the inlining.

Differential Revision: https://phabricator.services.mozilla.com/D157423

servo/ports/geckolib/glue.rs

@@ -5721,6 +5721,9 @@ pub extern "C" fn Servo_CSSSupports(
 }
 
 #[no_mangle]
+// Work around miscompilation when cross-LTO somehow inlines this function.
+// (bug 1789779)
+#[inline(never)]
 pub unsafe extern "C" fn Servo_NoteExplicitHints(
     element: &RawGeckoElement,
     restyle_hint: RestyleHint,